Two-dimensional materials with new physical phenomena are gaining popularity due to their unique properties. In recent years, a new family of layered compounds inspired by the minerals valleriite and tochilinite which are composed of alternating quasi-atomic sheets of transition metal chalcogenides (sulfides and selenides of Fe, Fe–Cu and other metals) and hydroxides of Mg, Al, Fe, Li, etc., assembled via electrostatic interaction, has arisen as a new synthetic platform for 2D materials. In this work, we synthesized a new promising material composed of alternating quasi two-dimensional sulfide Cu_4−xS₂ (x = 1–1.5) and hydroxide (Mg_1−yAl_y)(OH)₂ (y ∼ 0.25) sheets as multilayer flakes with a lateral size of 1–2 μm and a thickness of several tens of nm. The reliable formation of the material was ensured by an excess of aqueous sodium sulfide along with some quantity of Al salt, which was necessary for the self-assembly of the sulfide and hydroxide sheets driven by their opposite electric charges. A series of samples with varying Al/Mg ratios were examined using TEM, EDS, SAED, XRD, XPS, Raman and UV-vis-NIR spectroscopy. Using the Rietveld refinement procedure, the crystal lattice was determined to resemble the space group Pm1 with cell parameters a = b = 3.89 Å and a = b = 3.03 Å for sulfide and hydroxide parts, respectively, and the common parameter c = 12.03 Å. XPS and Raman spectra agree with the chalcocite-like sulfide layers containing Cu⁺ cations, monosulfide anions and few, if any, S–S bonds. UV-vis-NIR spectra show indirect transitions of 0.8 eV and considerable absorption in the near-infrared region. Thermogravimetry and differential scanning calorimetry studies under an Ar atmosphere suggest a slightly endothermic process and a phase transition at 90 °C accompanied, as suggested by conductivity measurements, by a metal–semiconductor transition; the main destruction with a loss up to 15 wt% occurs at ∼510 °C, due to decomposition of hydroxide layers similar to layered valleriite and tochilinite. The (thermo)electrical data show that, contrary to valleriite, which is an n-type semiconductor with mediocre thermoelectric performance, the proposed material is a heavily doped p-type semiconductor exhibiting good thermoelectric efficiency. The new member of the valleriite family of heterolayered quasi-2D materials demonstrates therefore essentially novel promising properties.

中文翻译：

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一种由交替的硫化铜和（Al，Mg）氢氧化物分子片构成的新材料：水热合成和选定的特性


具有新物理现象的二维材料由于其独特的特性而越来越受欢迎。近年来，受矿物 valleriite 和 tochilinite 的启发，一个新的层状化合物家族已经出现，它们由过渡金属硫属化物（Fe、Fe-Cu 和其他金属的硫化物和硒化物）和 Mg、Al、Fe、Li 等氢氧化物交替的准原子片组成，通过静电相互作用组装，作为 2D 材料的新型合成平台。在这项工作中，我们合成了一种新的有前途的材料，由交替的准二维硫化物 Cu _4-xS₂ （x = 1-1.5） 和氢氧化物 （Mg _1-yAl_y）（OH）₂ （y ∼ 0.25） 片材组成，作为多层薄片，横向尺寸为 1-2 μm，厚度为几十纳米。过量的硫化钠水和一定量的铝盐确保了材料的可靠形成，这对于硫化物和氢氧化物片的自组装是必需的，由它们的相反电荷驱动。使用 TEM、EDS、SAED、XRD、XPS、拉曼和 UV-vis-NIR 光谱检查了一系列具有不同 Al/Mg 比率的样品。使用 Rietveld 精修程序，确定晶格类似于空间群 P m1，硫化物和氢氧化物部分的单元参数分别为 a = b = 3.89 Å 和 a = b = 3.03 Å，公共参数 c = 12.03 Å。 XPS 和拉曼光谱与含有 Cu⁺ 阳离子、一硫化物阴离子和少量（如果有）S-S 键的辉铜矿状硫化物层一致。UV-vis-NIR 光谱显示 0.8 eV 的间接跃迁，并在近红外区域有相当大的吸收。Ar 气氛下的热重分析和差示扫描量热法研究表明，正如电导率测量所表明的那样，存在轻微吸热过程和 90 °C 的相变，并伴有金属-半导体转变;损失高达 15 wt% 的主要破坏发生在 ∼510 °C 时，这是由于氢氧化物层的分解类似于层状钙镁石和栉石。（热）电数据表明，与热电性能一般的 n 型半导体 valeriite 相反，所提出的材料是一种表现出良好热电效率的重掺杂 p 型半导体。因此，异质层准 2D 材料 Valleriite 家族的新成员基本上展示了新颖的有前途的特性。